Recent rates of sedimentation on irregularly flooded Boreal Baltic coastal wetlands: Responses to recent changes in sea level

Abstract

Boreal Baltic coastal wetlands differ markedly from temperate salt marshes by their generally low maximum elevation (between 0 and 1m above m.s.l.), low seaward gradients and the irregular nature of flooding that is characteristic of the NE Baltic Sea coastal region. As a result of these factors these wetlands have been considered to be threatened by future sea level rise. This study presents results for two Boreal Baltic coastal wetland sites in Estonia using the 210Pb and 137Cs radiometric dating methods to investigate the sedimentary development of these coastal systems. Recent coastal evolution has been largely driven by continuing glacio-isostatic adjustment (GIA), with maximum rates of 2.8mmyr−1 around the NW Estonian coast and the inherited geomorphological setting of generally flat-lying coastal topography, resulting in coastal emergence. Broad agreement exists between calculated rates of sedimentation identified within the core sequences. Average rates of sedimentation using the 210Pbexcess CF:CS (or ‘simple’) model range between 0.2 and 1.3mmyr−1. These rates are corroborated using 137Cs, which also suggests an increase in sedimentation rates during recent decades approaching maximum values for current land uplift. Additionally, the 210Pbexcess CRS model reveals periods of sedimentation greatly in excess of these values in response to coastal flooding from known storm activity. This study indicates that changes in sea level caused by variations in atmospheric pressure and storm surges can contribute a significant sedimentary component, which coupled with GIA processes has driven coastal wetland development/emergence and the historical progradation of these wetland systems. The recent acceleration in the rate of global sea-level rise may subtly alter this relationship. However current rates of GIA and sedimentation will continue to maintain the progradation of Boreal Baltic coastal wetlands in the coming decades.